Certain therapeutic substances, such as for example adrenaline, can be degraded by prolonged exposure to light with a result that their therapeutic effect is diminished or lost. Previously this has been overcome by disposing the syringe or cartridge in a housing which is opaque to at least the primary waveband of light responsible for the degradation. Alternatively, the device has itself been stored within an outer container which provides a tight shielding or filtering effect. However, the requirement to shield the substance from the light is in direct conflict with a requirement that the user be able to inspect the state of the therapeutic substance within the syringe before making the injection to check that it has not discoloured or leaked out. In the first type of injection device this is not possible and, in the second, it is possible but only at the expense of having to provide a separate outer container.